This invention generally relates to electric drive systems for vehicle components. More particularly, this invention relates to a system including a stepper motor that provides driving torque to a selected vehicle component.
Drive systems for vehicles typically include an internal combustion engine that provides driving torque through a transmission to driven wheels on a vehicle. Alternate arrangements have been proposed that include electric motors providing driving torque to driven wheels. In such situations, gear reduction assemblies have been required between the motors and the driven wheels because of the difference in rotational speeds required. Electric motors typically need to rotate at very high speeds to achieve the desired horsepower or torque necessary to drive the vehicle wheels. The wheels need to rotate at much lower speeds than the rotating components of the electric motors. Gear reduction assemblies, such as planetary gear arrangements, have been inserted between the electric motors and the driven wheels to provide the necessary gear reduction ratio so that the wheels are driven at the appropriate speed with the desired amount of torque.
Such arrangements, while having proven useful in some situations, are not without drawbacks and shortcomings. One major drawback associated with such arrangements is that the gear reduction assemblies introduce additional complexity, material cost, and weight to the vehicle. Further, it is often difficult to incorporate such arrangements within the typical packaging constraints of a vehicle. Modifying the vehicle chassis or other conventional vehicle components has proven prohibitively expensive for incorporating many proposed electric drive systems.
There is a need for improved arrangements where electric power can be used to provide driving torque without the difficulties of accommodating the additional gear reduction assemblies that have been commonly proposed. This invention addresses that need by providing a unique, electrically powered driving arrangement incorporating an electric motor that can be directly coupled to a driven member.
In general terms, this invention is an assembly that includes a stepper motor that provides driving torque directly to a selected driven member. No gear reduction is required between the motor output and the driven member and, therefore, the inventive arrangement can be much more readily incorporated onto a vehicle within typical packaging constraints. Additionally, eliminating the need for the additional gear reduction assembly provides cost savings and other system economies.
An example assembly designed according to this invention includes a wheel mounting member. A rotatable member is associated with the mounting member to rotate with the wheel. A stepper motor has a rotor and a stator. An output of the rotor is directly coupled to the rotatable member such that rotation of the rotor relative to the stator provides driving torque to the wheel.
With the inventive arrangement, the stepper motor can be operated in a first mode to provide driving torque to the wheel. The stepper motor can also be operated in a second mode where the motor applies a braking force to resist rotation of the wheel.
In one example embodiment, the stepper motor also functions as a parking brake when the motor is selectively powered to provide a parking brake function.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.